Abstract

This study is dedicated to link the nanoscaled pore space of carbons, prepared by hard-templating of meso-macroporous SiO₂ monoliths, to the corresponding nanoscaled polyaromatic microstructure. Two different carbon precursors were used, which generally exhibit markedly different carbonization properties, i.e. a graphitizable pitch and a non-graphitizable resin. The micro- and mesoporosity of these monolithic carbons was studied by the sorption behaviour of a relatively large organic molecule (para-xylene) in comparison to typical gas adsorbates (Ar). In addition, to obtain a detailed view on the nanopore space small-angle neutron scattering (SANS) combined with in-situ physisorption was applied, using deuterated p-xylene (DPX) as a contrast-matching agent in the neutron scattering process. The impact of the carbon precursor on the structural order on an atomic scale in terms of the size and the disorder of the carbon microstructure, on the nanopore structure and on the template process is analysed by special evaluation approaches for SANS and wide-angle X-ray scattering (WAXS). The WAXS analysis shows that the pitch-based monolithic exhibits a more ordered microstructure consisting of larger graphene stacks and similar graphene layer sizes compared to the monolithic resin. Another major finding is the discrepancy in the accessible micro/mesoporosity between Ar and deuterated p-xylene, which was found for the two different carbon precursors (pitch, resin), which can be regarded as representatives in regard to carbon precursors in general. These differences essentially indicate that physisorption using probe gases such as Ar or N₂ can provide misleading parameters if to be used to appraise the accessibility of the nanoscaled pore space.

Keywords: small-angle neutron scattering; pore structure; carbon; microstructure; adsorption

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Badaczewski, F.; Loeh, M.; Pfaff, T.; Wallacher, D.; Clemens, D.; Smarsly, B. Beilstein Arch. 2019, 2019114. doi:10.3762/bxiv.2019.114.v1

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